Omni-Roach: A legged robot capable of traversing multiple types of large obstacles and self-righting

Authors: Jonathan Mi, Yaqing Wang, Chen Li · ICRA 2022

Licences

Open Access
Paper: CC BY 4.0

Everything below draws on the full paper under its CC BY 4.0 licence; its figure is credited to the authors.

TL;DR

One small RHex-style robot combines a rounded shell, wings and an active tail to pass pillars, bumps, gaps and grass-like beams and to self-right, using strategies learned from cockroaches.

Why it matters

Search and rescue in rubble, forest-floor monitoring and planetary exploration need robots that push through obstacles rather than steer around them. The paper shows several body-shape and appendage strategies can be integrated into one small robot and tested on each obstacle type.

Problem

Robots navigate well by avoiding obstacles but struggle in 3-D terrain cluttered with large obstacles, where they must physically interact with them. Earlier work from the same lab found separate strategies for pillars, bumps, gaps, flexible beams and self-righting, but no single robot combined them.

Proposed solution

Omni-Roach is a six-legged RHex-class robot with compliant legs, a rounded shell that passively deflects off pillars and rolls into gaps, a top shell that opens as two wings for self-righting, and a tail with pitch and yaw used to pitch the body up and to tap the ground. Two prototypes were built: v1 (1.8 kg, C-shaped legs) and a smaller v2 (0.75 kg, S-shaped legs, faster motors, longer relative tail).

Key insights

The rounded body deflected the robot past pillars 100% of the time with no sensing or active control
Without the tail, both versions could not pitch up enough to climb a bump, and v1 got stuck pitching up against beams
In beam tests, a tail pointed down and oscillated in yaw rolled the body into the gap and broke frictional and interlocking contact, and was the only mode that traversed at all four approach angles
A static downward tail traversed beams only at 15° to 45° approach angles, suggesting one role of tail oscillation is to adjust approach angle
The v2 gains are attributed to longer relative legs (14% to 25% of body length), a longer relative tail (54% to 73%) and about 4× the stride frequency, with leg force to body weight only falling from 1.6 to 1.4

Main results

v2 climbed a bump of 2.5× hip height with 80% success, versus 1.5× hip height for v1
v2 crossed a gap of 75% body length (15 cm) with the tail at home, versus 48% (17 cm) for v1; tail motion did not improve gap crossing for either version
v2 traversed beams with a gap of 65% body width (12 cm, about 50° body roll), versus 91% (21 cm, about 24° roll) for v1
Self-righting in 4.0 s with 100% success for v2, and 90% success within 4 s for v1, on flat ground
Pillar spacing is given as 1.1× body width in the abstract and as 1.08× body width in the closing section (four pillars spaced 20 cm, v2 width 18.5 cm)
Over 160 beam trials (10 per tail mode and approach angle), yaw-oscillating the downward tail cut average traversal time by 30% versus the static downward tail at 15°, 30° and 45°

Limitations

The robot is manually controlled between locomotor modes; the authors name vision and contact-force sensing for autonomous transitions as future work
Leg and tail motors are too slow for dynamic gap traversal, so the tail does not help cross gaps
The rounded shell that helps with pillars and beams deflects the robot away from bumps; the authors propose a shape-morphing shell
All tests were on simple lab testbeds (aluminium pillars and bumps, acrylic beams on torsion springs, pegboard with sandpaper), with self-righting tested on flat ground only

Field impact

Finalist for the ICRA 2022 Outstanding Locomotion Paper award, with 20 citations. The paper does not state a release of code or design files; a supplementary movie accompanies it.

Abstract

Robots excel at avoiding obstacles but still struggle to traverse complex 3-D terrain with cluttered large obstacles. By contrast, insects like cockroaches excel at doing so. Recent research in our lab elucidated how locomotor transitions emerge from locomotor-environment interaction for diverse locomotor challenges abstracted for complex 3-D terrain and what strategies overcome these challenges. Here, we build on these fundamental insights to develop a cockroach-inspired legged robot, Omni-Roach, that integrates these strategies for multi-functional locomotion. The robot is based on the RHex-class design with six compliant legs and features a rounded body shape with two wings that can open, an active tail with pitch and yaw degrees of freedom. Through two development and testing iterations, our robot was capable of overcoming all locomotor challenges with high performance and success rate. It traversed cluttered rigid pillars only 1.1× robot body width apart, a 2.5× hip height bump, a 0.75× body length gap, densely cluttered flexible beams only 65% its body width apart, and self-righted within 4 seconds. Systematic experiments on tail use and approach angle for beam traversal revealed that an active tail pointed downward and tapping against the ground helps roll the body into the gap and break frictional and interlocking contact to traverse.

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